A flash memory is recently used in communication instruments, AV (audio visual) instruments, and other instruments in various fields. Data in a flash memory is erased in units of a block, which is a group of multiple memory cells. In some cases, therefore, a write unit size and an erasure unit size may differ from each other. For example, a write is performed in units of a block having several bytes while an erasure is performed in units of a block having several tens of bytes to several kilobytes.
Due to a characteristic that a flash memory cannot be overwritten, data is additionally written into a block in a sequential manner for data management purposes. As such being the case, when, for instance, a block is filled as a result of repeated additional write into the block, an unoccupied block (an empty block) is prepared by erasing data from a block other than the filled block for the purpose of copying valid data (this process will be hereinafter referred to as the reorganization process).
During execution of the reorganization process, a data erasure process and a copy process are intensively performed with respect to blocks. A processing load on the entire storage system having a flash memory may increase. Thus, access to data during the reorganization process is likely to be blocked.
Storage apparatus previously proposed, for instance, in Patent Literature 1 performs the reorganization process in a standby state in which no access is made. When data is accessed during the reorganization process, the storage apparatus interrupts the reorganization process, and then resumes the reorganization process upon termination of access. In this manner, the storage apparatus reduces the possibility of access to data being blocked during the reorganization process.
The inventors of the present application have found the following. The storage apparatus proposed in Patent Literature 1 needs to perform the reorganization process itself. Therefore, when a period of time when processing load increases due to the reorganization process gets longer, overall system performance may deteriorate.